The anode layer ion sources are well known having been implemented in industrial applications and ion thrusters for many decades. FIG. 1 shows a 3D view of a prior art anode layer ion source and FIG. 1A shows a section view of this prior art ion source. As shown in FIG. 1, the ion emitting racetrack of an anode layer ion sources can be extended in one axis to have long straight-away sections. In practice, these sources have been made several meters long. This is possible because electrons are confined in an endless closed drift around the racetrack. The closed drift electron confinement produces a uniform discharge around the racetrack and subsequently a uniform ion beam 113 is emitted from the slit 112. As shown in FIG. 1A, the prior art anode layer ion source creates the closed drift confinement using magnet 101, center pole 131 and outer pole 130 such that magnetic field 115 crosses from the center pole to outer pole around the racetrack 112. An annular anode 102 is positioned under the poles and power supply 114 generates the electric field to operate the source. In long ion sources, source gas 107 must be distributed along the length of the source. This is shown for source 100 as manifold 106 and distribution holes 110. An anode layer ion source is differentiated from other closed drift ion sources by the spacing of the gap between the center and outer poles and the gap between the poles and the anode. In an anode layer ion source, these gaps are made small, on the order of 2-3 mm so that the electron confinement region is too small for a conductive plasma to light. In this way an anode layer ion source can be operated in a collimated, high voltage mode. In the collimated mode, the anode voltage can be in the 1000's of volts and the emitted ions are efficiently directed out of the source. If the gaps are larger, a conductive plasma can be sustained in slit 112 and the electric fields shift around this plasma. In this so called ‘diffuse’ mode, pole sputtering is considerable and the maximum source voltage drops down to typical closed drift ion sources, in the 100's of volts. While operating in the diffuse mode can be useful, the design of anode layer ion sources and suggested operating parameters are intended to keep the sources running in the collimated mode. It is important to note that the gas pressure in the slit is also important to the operating mode. If the pressure is too high, and the resulting mean free path too short, an anode layer ion source can operate in the diffuse mode even if the pole gaps are small. Typically, to avoid diffuse mode operation, anode layer ion sources are operated at less than 1 Pa for this reason.
While prior art anode layers sources are useful, the racetrack shape of the ion emitting slit is not ideal. When the racetrack ion beam is directed at an angle to a substrate, the two parallel straightaway beams of the racetrack hit the substrate after different travel distances. Given there are collisional energy losses as ions travel to the substrate, a longer travel distance lowers the ion beam energy and the two straight-away beams hit the substrate at different energies. Additionally, the chamber space needed to fit the angled ion source and racetrack beam is larger than desired.
Thus, there exists a need for linear ion emitting slit ion source to overcome the limitations of the racetrack-shaped slit ion source.